Conventionally, as fabrication methods of a metallized ceramics substrate, co-firing method and post-firing method have been commonly known. Co-firing method means a method for fabricating a metallized ceramics substrate precursor by forming a conductive paste layer on a non-fired ceramics substrate precursor, the so-called “green sheet” and firing this thereafter. In this method, firing of the green sheet and the conductive paste layer is done simultaneously. Post-firing method, on the other hand, means a method for fabricating a metallized ceramics substrate precursor by forming a conductive paste layer on a sintered ceramics substrate obtained by firing a green sheet, and firing this thereafter. In this method, firing the green sheet and conductive paste layer is sequentially done. Various fabrication methods of a metallized ceramics substrate using post-firing method are known, one of the examples is disclosed in Patent document 1.
Both of the above methods are capable to make wiring on the ceramics substrate; the obtained substrate is mainly used as a substrate for mounting semiconductor device. Such a substrate on which semiconductor devices are mounted is required to improve the accuracy and fineness of a wiring pattern with the miniaturization of parts to be mounted.
When wiring pattern is formed by co-firing method, the green sheet tends to unevenly shrink at a time of firing. For example, if a square green sheet is sintered, slight shrinkage is caused such that center portion of each side of the square inwardly warps and the square shape is deformed into a star-like one. So, if many wiring patterns with the same shape are formed on one green sheet, inevitably, the shape of patterns is slightly changed depending on the area where patterns are formed.
Meanwhile, in case of forming wiring pattern by post-firing method, the wiring pattern is formed by directly applying a conductive paste on a sintered ceramics substrate and drying thereof, then firing the paste after drying. When firing the wiring, conductive paste layer shrinks in a thickness direction but it does hardly shrink in a planar direction, problems like shape of pattern is changed depending on the area to be formed as seen from co-firing method cannot be caused. Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 8-239286